Gas lubricated barrier seal

ABSTRACT

A double, back to back oriented mechanical end face seal arrangement for use in sealing pumps or other devices used in fluid transfer of toxic or corrosive fluid has an intermediate buffer fluid chamber into which a relatively inert gas, such as nitrogen, is provided for use as a buffer fluid, and is maintained at a pressure which exceeds the process fluid pressure by at least 10 p.s.i. Each seal has a primary ring and a mating ring with gap maintaining means, such as spiral pumping grooves, formed in one of the rings which are shaped and dimensioned to pump the buffer gas through the first seal from the intermediate chamber into the process fluid chamber against the process fluid pressure and through the second seal from the intermediate chamber into the environment external to the housing and sealing area, thus avoiding the escape of the process fluid into the intermediate buffer chamber and thereby to the atmosphere. The inboard seal includes a first secondary sealing means disposed between one seal ring and the housing for sealing therebetween and a second secondary sealing means, disposed between the other seal ring and the shaft for sealing therebetween, the first and second secondary sealing means, which may comprise O-rings, each defining the boundary between the intermediate chamber and the process fluid chamber. The first and second secondary sealing means of the first rotary mechanical end face seal are sized and disposed to define radial walls in the back radial surfaces of each seal ring to thereby present essentially an equal area at an approximately identical radius, such that essentially the same mount of buffer fluid pressure acts on the back radial surfaces of each ring of the first rotary mechanical and face seal but in opposite directions and, on the process fluid side, the identical process fluid pressure acts on opposite sides of a portion of the respective rings of the first rotary mechanical end face seal essentially eliminating thrust forces acting on the first rotary mechanical end face seal.

This is a continuation of application Ser. No. 07/946,914, filed on Sep.18, 1992, now U.S. Pat. No. 5,375,853.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to mechanical end face seals andmore particularly relates to dual mechanical end face seals for use insealing toxic or corrosive fluids.

2. Background Art

Mechanical end face seals have long been used to seal the space betweena housing and a relatively rotating shaft which passes through thehousing. Such seals usually include a primary ring which has a generallyplanar radial sealing face and is fixed to and mounted in the housing.The primary ring may be mounted on the housing by a secondary seal, suchas an O-ring. In addition, the seal includes a mating ring which ismounted on the shaft for rotation therewith. Like the primary ring, themating ring has a generally planar radial sealing surface. The matingring radial surface is disposed in opposing relationship to the primaryring and the two radial surfaces are biased into sealing engagement.These types of seals are described in U.S. Pat. No. 4,212,475 issued toJ. Sedy and assigned to the same assignee as the present invention.

Many configurations are known for utilizing either a single seal or aplurality of mechanical end face seals used together for specific sealapplications. Single seal configurations are adequate for most sealingapplications, including pumps, compressors, mixers and the like whenutilized to seal fluids which are benign with respect to theenvironment. More recently, however, rising concern over pollution andtoxic emissions has culminated in regulatory directives calling for"zero emissions" of toxic fluids into the environment. Thus, a need hasarisen in the seal industry for seals which can provide a solution tothe toxic fluid emission problem. Possible solutions which approached ormet the zero emission standard have been proposed. These proposals haveresulted in two broad categories of seal design, one type being known as"wet" double seals and the other type being magnetic drive pumps.

An example of the "wet" seals can be found in U.S. Pat. No. 4,290,611,issued to J. Sedy and also assigned with the present invention to acommon assignee. That patent describes and illustrates a "double seal"arrangement (FIG. 1) which utilizes two mechanical and face sealsoriented back to back along a drive shaft. The two seals define achamber between them into which a lubricant buffer fluid is continuouslycirculated for cooling the seal rings. The buffer fluid, usually oil, isat a pressure generally 5-20 p.s.i. above the sealed process fluidpressure. The arrangement is described as being most desirable forsealing corrosive liquids because the metal parts of the seal areisolated from the process fluid by use of a non-corrosive buffer liquid.

The seal arrangements described in the '611 patent work well in certainapplications, but cannot be used in applications where the sealedprocess fluid is a gas or where the sealed fluid is a liquid in whichcontamination by the buffer fluid cannot be tolerated. Generally, oil isused as a buffer fluid but many process fluids are reactive with theoil, or contamination by the oil in the process fluid is not desirable.

More recently, magnetic drive pumps have been developed which provide a"zero emission" capability, albeit at greater expense. For these typesof applications, the shaft does not extend through the housing, but theshaft terminates at the housing wall thus eliminating the openingthrough which the shaft would extend. The impeller which pumps the fluidis encased in the housing chamber and is connected to a first set ofmagnets. The impeller is driven by a second set of magnets which aredisposed externally of the chamber. Rotation of the externally disposedmagnets by an external motor, in turn, rotates the magnets connected tothe impeller inside the encasing housing chamber. Since the housingchamber is completely encased and does not include a shaft opening, noleakage of fluid can take place through the chamber wall under normaloperating conditions.

The magnetic drive pumps are more complex and expensive thanconventional mechanical end face seals. The magnets which drive theimpeller are of special construction and special bearings are necessaryto maintain the alignment of the magnets and the impeller shaft whichprovides the connection to the impeller. Moreover, magnetically drivenpumps require a coolant fluid stream to remove waste heat generated bymagnetic losses and by friction.

What is required by the industry is an inexpensive, easily constructed,seal which has a "zero emission" capability and which meets theregulations for toxic fluid emissions in an increasingly regulatoryenvironment for general use.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides for a seal arrangement forsealing against leakage of process fluid under pressure within a housingalong a rotatable shaft extending through a wall of the housing, theseal arrangement generally comprising a first rotary mechanical end faceseal including a stationary seal ring for sealing connection to thehousing and a rotary seal ring for sealing connection to the shaft, eachring having an annular generally radial sealing face in relativelyrotating, mating sealing relation with the face of the other ring, asecond rotary mechanical end face seal including a stationary seal ringfor sealing connection to the housing and a rotary seal ring for sealingconnection to the shaft, each ring having an annular generally radialsealing face in relatively rotating, mating sealing relation with theface of the other of the rings, the first and second rotary mechanicalend face seals being axially spaced along the shaft and arranged todefine, with the housing, an intermediate chamber therebetween, eachseal including means biasing one of the rings toward the other tomaintain the annular sealing faces of each seal ring in relativelyrotating sealing relation the relatively rotatable sealing rings of thefirst end face seal having one annular circumference of the sealingfaces exposed to the process fluid to be sealed within the housing, andthe other annular circumference of the sealing faces exposed to theintermediate chamber, the relatively rotatable sealing rings of thesecond seal having one annular circumference of the sealing facesexposed to the intermediate chamber, and the other annular circumferenceof the sealing faces exposed to the ambient environment external thehousing, the intermediate chamber being in communication with theinterior of the housing containing process fluid under pressure onlyacross the relatively rotating, mating, sealing faces of the firstrotary mechanical end face seal, the intermediate chamber being incommunication with the ambient environment external to the housing onlyacross the relatively rotating, mating, sealing faces of the secondrotary mechanical end face seal, the intermediate chamber includingmeans for connection to a source of relatively inert gas at a pressureexceeding the pressure of the process fluid present at the circumferenceof the annular seal faces of the first rotary mechanical end face sealrings.

In one embodiment of the invention, the radial face of one of the ringsof the first rotary mechanical end face seal includes a plurality ofspiral grooves extending from the circumference exposed to therelatively inert gas in the intermediate chamber, which may be the outercircumferential diameter of the seal rings, partially toward thecircumference exposed to the process fluid in the interior of thehousing, which may be the inner circumferential diameter, and definingon the face an annular dam adjacent the circumference exposed to theprocess fluid in the housing, or the outer circumferential diameter. Theprimary rings of both seals in the preferred form rotate together withthe shaft. The preferable buffer gas is nitrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section, axially, of a housing and shaft incorporatinga preferred embodiment of the invention.

FIG. 2 is an end view of one of the sealing rings of the preferredembodiment of the invention.

FIG. 3 is an end view of the other of the sealing rings of the preferredembodiment of the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

FIG. 1 illustrates a seal generally indicated at 10 constructed inaccordance with the preferred embodiment of the present invention. Theseal is designed to seal toxic fluids within a housing 12 so thatliterally "zero emission" of the sealed toxic process fluid is achievedand literally no process fluid escapes to the ambient environmentexternal to the housing. The housing includes a shaft passage 14 whichaffords a shaft 16 to extend through the housing 12. The housing 12 maycomprise a stuffing box, such as has used in the past for the stuffingof packing, the packing having been pressed against the shaft tominimize leakage through the housing and shaft interface. The housing 12further separates an inner chamber 18 containing process fluid from theambient environment 20 external the housing which generally comprisesthe atmosphere.

The seal arrangement of the preferred embodiment is disposed adjacentthe housing 12 and generally within the stuffing box formed by thehousing 12. A seal arrangement including double, back to back oriented,axially-spaced rotary, mechanical end face seals of the spiral groovetype each have opposed ring portions respectively secured to the housing12 and shaft 16. The seals are similar in most respects to the typeshown and described in aforementioned U.S. Pat. No. 4,212,475.

The seal arrangement comprises a first seal, generally indicated at 22,adjacent the process fluid chamber 18 and enclosed by the wall ofhousing 12, and a second seal 24 adjacent the ambient environment 20external to the seal arrangement and to the housing. The first andsecond seals 22 and 24 define an intermediate chamber 26 between them.The chamber 26 is surrounded by a liner assembly 28, which together witha flanged gland plate 30, define the other end wall of the intermediatechamber 26. The shaft 16 includes a sleeve assembly 32 which surroundsthe shaft and which is a base on which the seal rings rest and aroundwhich the seals 22, 24 are disposed.

The first seal 22 includes a pair of annular rings comprising a rotatingseal ring 36 and a stationary seal ring 40. Rotating seal ring 36 has aradially extending face 38 and a radially extending shoulder 37 disposedat the outer circumference. The rotating seal ring 36 is opposed to thestationary seal ring 40 having a radially extending face 42 opposite theface 38 of the rotating ring 36. The stationary seal ring 40 is alsoreferred to herein as the mating ring 40 and the rotating seal ring 36is also referred to herein as the primary ring 36. As will be describedbelow, this relationship is not the only configuration of the seal ringspossible in practicing the present invention. The primary ring 36 shownin the preferred embodiment is fixed relative to the shaft 16 androtates therewith. The primary ring 36 is sealed against the sleeve 32,but is shaped and dimensioned to have freedom of motion axially relativeto the sleeve 32 and shaft 16 at least to a limited degree.

As shown in FIG. 1, the primary ring 36 is fixed in the rotationaldirection relative to the sleeve assembly 32 for rotation therewith.However, it is possible in an alternative embodiment (not shown) to havethe primary ring fixed relative to the housing, and the mating ring tobe rotating with the shaft. In that embodiment, suitable modification ofthe arrangement within the skill of a person knowledgeable in the artwould be necessary to accommodate such an alternative design.

The mating ring 40 has a face 42 in facing relation to face 38 of theprimary ring 36. When they are brought together, the faces 38 and 42interface and provide the sealing function of the seal 22. The interfaceneed not be co-extensive with both of the faces 38 and 42, but as isshown in FIG. 1, the face 38 of the primary ring 36 extends only partway across the face 42 of the mating ring 40.

The interface between faces 36 and 42 is in the shape of an annulardisc, with the shaft 16 extending through the central aperture of eachring. As shown in FIG. 2, the mating ring 40 includes a plurality ofspiral grooves 44 disposed partially across the face 42 of ring 40, andextending from the outer circumferential diameter toward the innercircumferential diameter thereof. The grooves 44 are also illustrated inphantom in FIG. 1 but the depth of the grooves is exaggerated forillustrative convenience. As is described in aforementioned U.S. Pat.No. 4,212,475, the depth of the grooves is on the order of 50 to about400 microinches. In the preferred embodiment, the grooves are about 300microinches in depth.

Referring to FIG. 2, grooves 44 are circumferentially and evenly spacedand are separated by plural radially extending lands 45. An ungroovedsurface at the inner diameter of seal face 42 defines a sealing dam 46which, in cooperation with the opposed face 38 of the primary seal ring36, provides a static seal when the shaft 16 is not rotating. When shaft16 is not rotating, the process fluid is sealed by a hydrostatic filmbetween the primary and mating rings at the sealing dam 46. When theshaft starts rotating, interaction of the grooves 44 with the rotatingface 38 of ring 36 normally pumps a fluid present in the chamber 26radially inwardly across the seal faces 38, 42, causing the seal facesto open slightly to present a gap between the faces. The fluid which ispumped into the gap maintains a non-contacting condition between theseal faces and also acts to cool the faces of excess heat which isgenerated by shear frictional forces of the relatively rotating sealfaces.

At the end of the mating ring 40 opposite from that of the face 42,(FIG. 1), there is a depression or bore 41 which is disposed to receivea retainer pin 43 to fix ring 40 relative to the liner assembly 28 andto the housing 12. The retainer pin is generally an element of the linerassembly 28 and may be an integral element which is machined as aportion of the assembly. Preferably, the retainer pin 43 is a separateelement which is press fitted into the liner during manufacture. AnO-ring 47 is used to seal the mating ring 40 to the liner assembly 28. Ashoulder in the outer circumferential wall of the primary ring 40provides for a radially extending annular wall 39 which abuts acorresponding radially extending wall of the liner assembly.

The seal 22 is shown having the grooves 44 at the radially outerdiameter adjacent the intermediate chamber 26 and the sealing dam 46 atthe radially inner diameter adjacent to and being exposed to the processfluid within the chamber 18. The principles of the invention, however,are applicable to seals having the grooves at the inner diameter and thedam at the outer diameter, with the inner diameter grooves being exposedto the buffer fluid within the intermediate chamber. Such an alternateembodiment (not shown) may require a different configuration of therings, e.g., with the mating ring rotating and the primary ringstationary. It is within the skill of those in the art to design analternative configuration with the stated characteristics upon achievingan understanding of the present invention.

The sleeve assembly 32 includes a shaft sleeve 48 which fits upon theshaft 16. Sleeve 48 includes a thicker portion 50 at one end, which isrecessed to provide a thinner portion 51 at the other annular end of thesleeve 48. The sleeve 48 is fixed to the shaft 16 by a collar 52 securedto the thinner portion 51 of sleeve 50 by a bolt, as will be explainedbelow. Alternatively, a drive key arrangement (not shown) may be used tosecure shaft sleeve 48 to the shaft 16. Sleeve assembly 32 furtherincludes an O-ring 56 for sealing between the thicker portion 50 and theshaft 16, and another O-ring 58 for sealing between the primary ring 36and the thicker portion 50. The recessed thinner portion 51 of sleeve 48accommodates assembly of other portions of the seal arrangement, such asthe elements of the second seal 24.

The O-rings 56 and 58 are fit into appropriate grooves in the thickerportion 50, and the outer diameter O-ring 58 is shaped, sized andconfigured to permit axial motion of the primary ring 36. The O-ring 58is of a diameter as close as possible to the diameter of O-ring 47.O-rings of the same diameter enhances seal balance of the seal 22because it tends to equalize the forces which arise from the processfluid pressure which is present in chamber 18. The O-rings set theradial location of the boundary between the pressure of the buffer fluidand of the process fluid, as will be explained below. The O-rings 47,58thus define the balanced pressure acting on radially extending surfacesof each of the seal rings 36 and 40. The higher pressure buffer fluidacts on the radially extending walls 39 of seal ring 40 while asimultaneous and opposite force acts on the face of the seal ring 36which is opposite the seal ring 36 from the face 38. Because the annularwidths in the radial direction of the wall 39 and the non-contactingradial face of ring 36 present essentially an equal area at anapproximately identical radius, essentially the same amount of bufferfluid pressure acts on each of the rings albeit in the oppositedirections. On the process fluid side, the identical process fluidpressure acts on opposite sides of a portion of mating ring 40 and on aportion of primary ring 36. Thus, the pressure forces on each of therings cancel each other out, thereby essentially eliminating thrustforces acting on the seal 22.

Seal 24 also includes a pair of annular rings. One ring comprises astationary ring 60 having a radially extending face 62. The stationaryseal ring 60 is opposed to the other ring, rotating ring 64, also havinga radially extending face 66 opposite the face 62 of stationary ring 60.The stationary seal ring 60 of second seal 24 is also referred to as themating ring seal 60 and the rotating seal ring 64 is also referred to asthe primary seal ring 64.

Primary seal ring 64 is not identical in construction to the ring 36.For example, a recessed groove 68 in the primary seal ring end oppositethe seal face 66 provides accommodation for an O-ring 70 which sealsbetween the ring 64 and the thicker portion 50 of the sleeve 48. In manyrespects, including the disposition of the O-ring 70, the second seal 24is similar to the seal described and illustrated in aforementioned U.S.Pat. No. 4,212,475. In one important respect, however, seal 36 isdifferent from that of the seal described in that patent. The disclosurein the '475 patent describes the primary ring fixed to the housingwithin a retainer. However, in the preferred embodiment of the presentinvention, the primary ring 64 is rotating and the mating ring 60 isstationary. Different design considerations are applicable in eithercase. For example, the retainer of the seal in the patent includes anelongated inner diameter wall on which an O-ring seals against theprimary ring whereas in the present invention, the corresponding O-ring70 rests on the sleeve 48. Nevertheless, the teaching of the presentinvention is applicable to seal configurations having any of a number ofdesigns which may be within the purview of those having ordinary skillin the art.

Referring again to FIG. 1, a shoulder in the outer circumferential wallof the primary ring 64 provides for a radially extending annular wall72.

The mating ring 60 of seal 24 is also different from that of mating ring40. Mating ring 60 is an annular ring with an annular groove 77 disposedin the outer circumference for receiving an O-ring 75. The O-ring 75provides a seal between mating ring 60 and gland plate 30.

Referring to FIG. 3, where an elevation view of the seal face 62 of ring60 is illustrated, seal face 62 also includes a plurality ofcircumferentially spaced spiral grooves 74. The grooves extend partiallyacross the radial width of mating ring seal face 62 and are also shownin mating ring 60 of FIG. 1, the width being exaggerated forillustrative convenience. An ungrooved surface at the inner diameter ofseal face 62 defines a sealing dam 76 which, in cooperation with theopposed sealing face 66 of the primary ring 64, provides a static sealwhen the shaft 16 is not rotating, similar to the dam 46 of seal 22.During shaft rotation, the shaft 16 and primary ring 64 rotate relativeto the mating ring 60 and the interaction of the rotating face 66 ofprimary ring 64 and the spiral grooves 74 in seal face 62 acts to pumpthe buffer fluid within intermediate chamber 26 across the sealinterface of seal 24 and into the ambient environment 20.

Utilization of stationary mating rings 40, 60 together with the faces42, 62 including the spiral grooves 44, 74 respectively, is the reverseof most seal designs. It has been found, however, that whether the ringshaving the spiral grooves are disposed on a rotating ring, as in theseal described in aforementioned U.S. Pat. No. 4,212,475, or whether therings having the grooves are maintained stationary, as in the presentinvention, does not provide an appreciable difference in the amount ordirection of the pumping action on the fluid.

It is believed that a film of fluid rides together with the rotatingring, despite its relatively smooth, flat surface, and despite theabsence of the spiral pumping grooves on the rotating ring. Thephenomenon of the fluid film rotating on and with a smooth seal faceresults from a laminar flow, with the relative flow being provided tothe stationary liquid by the rotation of the faces 42,62 of rings 40,60.As the fluid film meets the faces 42,62 of mating rings 40,60, the fluidfilm is constrained by the grooves 44, 74 and is forced radiallyinwardly along a surface boundary layer on each face 42,62. Althougheach ring having the spiral grooves is retained stationary, the actionof the laminar flow is sufficient to pump enough fluid between the facesand create the gap between the faces during relative rotation betweenthe faces.

A biasing force is necessary to counteract the tendency to increase thegap created by the fluid. If the gap becomes too great, the leakage offluid from the high pressure side of the seal becomes excessive andneeds to be brought under control. Referring again to FIG. 1, a biasingforce is provided to each of the primary rings 36,64 by a single set ofplural springs 80 evenly disposed around the circumference of theannular primary rings 36, 64. Springs 80 press directly onto a pair ofdiscs 82,84 which abut the faces of each primary ring 36,64,respectively, which faces are opposite the sealing faces 42,62,respectively. Thus, the force of springs 80 counteracts the openingforce of the spiral grooves while the pressure forces acting on each ofthe rings 36,64 counteract each other.

The springs 80 are held in place by a retainer 90 having a cylindricalouter circumferential wall 92. The retainer 90 has an elongated innerwall 94 defining an annular space which at one end accommodates matingseal ring 40 of seal 22 and at the other end accommodates mating sealring 60 of seal 24.

Along a central portion of inner diameter wall 94, is an annular diskelement 96. In the preferred embodiment, the disk element 96 is integralwith the retainer 90. Disk element 96 includes a plurality of apertures98 which extend therethrough. The apertures 98 have a sufficiently largediameter to permit insertion of the springs 80 therethrough. Theretainer 90 and disk element 96 thus retain the springs 80 in bothcircumferential and radial positions. Even spacing of the springs 80around the circumference of disk element 96 provides an even bias on themating rings 40, 60 around the full circumference of the rings 40,60. Inthe preferred embodiment, there are four springs disposed at regular 90°intervals within the disk element.

The retainer 90 at an inner diameter of disk element 96 is adjacent thethicker portion 50 of sleeve 48. A plurality of set screws (not shown)extend radially through bores which are radially disposed in the diskelement separated from the axial apertures 98. The set screws impinge onthe outer circumferential surface of the sleeve, whereby the retainer 90becomes fixed in the axial and circumferential directions relative tothe sleeve 48. Thus, the retainer 90, disk element 96, primary rings36,64 and the springs 80, all rotate together with the shaft 16 duringoperation of the device in which the seal arrangement is used.

The inner diameter of the cylindrical retainer 90 further includesadjacent each end an internal groove 98 for receiving a snap ring 100.Each snap ring 100 fits within the groove 98 and provides a radiallyextending wall 102. Wall 102 of one snap ring 100 interfaces with wall37 of primary ring 36 to retain the ring within the retainer 90.Similarly, wall 102 of the other snap ring 100 interfaces with theradially extending wall 72 of primary ring 64 to retain the ring withinthe retainer 90. Under normal operating conditions, however, eachprimary ring is preloaded during assembly so that the walls 37,72 of therespective primary rings are separated from the snap ring walls 102.

As described above, a liner assembly 28 fits within the packing housingformed by wall 12 and encloses a portion of the arrangement, includingseal 22 and a part of the retainer assembly 90. Liner assembly 28comprises an inner diameter annular support flange portion 110 which isshaped and configured around its inner diameter to receive the matingring 40 of seal 22. Radially extending wall 39 of ring 36 closely abutsa corresponding radially extending wall of the flange portion 110.

The flange portion 110 further includes a plurality of axially extendingpin receiving bores 112 for receiving pins 43 to provide stationaryengagement between the flange portion 110 and the mating ring 40. Anannular groove 114 provides a sealing receptacle for receiving theO-ring 47 which seals between the liner assembly 28 and the primary ring36.

An outer diameter flange portion 120 of liner assembly 28 is attached tothe inner diameter support flange portion 110 by an elongated tubularportion 116. Tubular portion 116 has an outer diameter that fits withinthe housing wall 12, but does not necessarily seal against it. A fluidtight seal between liner assembly 28 and housing 12 is provided by anO-ring 122 which fits within a groove 124 in the outer diameter cornerbetween the outer diameter flange portion 120 and the tubular portion116. Groove 124 has a diameter at one of its axially extending wallswhich is identical to the outer diameter of the tubular portion 116, sothat it can be considered as an extension of the outer diameter wall oftubular portion 116. In this position, when a radially extending wall126 of outer flange portion 120 is brought flush with the wall ofhousing 12, the O-ring 122 is pressed against the housing wall to sealbetween the liner assembly 28 and the housing 12. Sealing load in theaxial direction is preferable to that in the radial direction becausethe liner can be more easily installed by sliding the tubular portionwith the packing housing.

The outer flange portion 120 preferably includes a connection to thewall of housing 12, as will be described below. Several bolts 130, shownin phantom, extend through a set of equidistantly disposed recessedbores 128, shown in phantom, in the radial wall of the outer diameterflange portion 120 to connect the liner assembly 28 to the flanged glandplate 30.

Gland plate 30 includes an inner diameter portion which has axiallyextending inner diameter sealing surface 132 against which the O-ring 75is sealed. The depth of groove 77 which is disposed in the outercircumferential diameter of mating ring 60 provides enough clearance toenable the mating ring 60 to be press fitted into the annular shoulderformed by surface 132. Together with the O-ring 75, a fluid tight sealis effected between the mating ring 60 and the gland plate 30.

Gland plate 30 includes an inlet port 134 and a passageway 136 for afluid connection between the intermediate chamber 26 and the inlet port134. The inlet port 134 is itself connected to and in fluidcommunication with a source of a gas which is non-hazardous to theenvironment but which is compatible with use of a specific processfluid. Any relatively inert gas, or a gas which is non-reactive with theprocess fluid, may be utilized as a buffer gas. Nitrogen gas ispreferable as a relatively inert gas because of its low cost and easyavailability, but a noble gas, such as argon, neon, or the like, mayalso be considered appropriate in certain applications. In a limitednumber of other applications, air may be used as the buffer fluid if itsuse is compatible with the process fluid.

Alternatively, a gas that is reactive with the process fluid may also beused in certain applications in which the reaction is desirable, such aswhen the buffer gas is to be added to the process fluid at some stage ofthe process fluid processing. As an example, the introduction of carbondioxide into the process fluid may be performed as part of the chemicalprocessing of the process fluid. When used in this way, closemeasurement of the amount of buffer fluid introduced into the processfluid is important, and a calculation of the buffer fluid volume pumpedinto the process fluid by the spiral grooves may be necessary to provideonly that amount of carbon dioxide which is necessary for the desiredchemical reaction to occur.

In the preferable environment, the buffer fluid gas is at a pressureexceeding the maximum expected process fluid pressure. Preferably, thesource of nitrogen provides a nitrogen stream to the inlet port 134 atabout 10 p.s.i. above the maximum process fluid pressure. The nitrogensource may be provided by any of a number of possible means. Forexample, for an application in a chemical plant, the nitrogen source maybe a piped-in line of nitrogen which results from by-products of variouschemical process and which is readily available throughout most chemicalplants. The pressure of the nitrogen supplied to the inlet port may beregulated to the desired level between the line source and the inletport.

Alternately, the source may be a bottled nitrogen source at highpressure which also requires a regulator for a supply of nitrogen at thedesired pressure. In the preferred embodiment, the inlet port isdisposed at the highest point of the gland plate 30 for convenientaccess but this is not necessary for operation and in otherconfigurations, it may be desirable to provide an inlet port at adifferent position and oriented at a different angle as befits aparticular application.

The collar 52 is axially disposed outside the immediate seal arrangementand provides a connection between the sleeve 32 and the shaft 16. Theaxial position of the sleeve 32 is important in providing clearance ofthe axially movable elements in each seal. To ensure that the sleeve isaxially disposed at the proper location, the collar in 52 is fit overthe sleeve 32 and connected thereto by set screws 140 shown in phantom.The set screws 140 extend through the sleeve 32 and into a predeterminedaxial bore 142 in the shaft 12, thereby connecting the three elementstogether and axially fixing each relative to the other.

The proper spacing of the sleeve 32 relative to the gland plate 30 andto the other elements of the seals 22,24 is effected by use of aplurality of spacers 144. Each spacer 144 is a right angled strip withtwo legs, one leg being connected to collar 52 and the other leg togland plate 30 by cap screws (not shown) which extend in threaded bores(not shown) appropriately disposed in the collar 52 and in the glandplate 30.

Spacer 144 is used only during assembly of the seal arrangement onto theshaft 16, and is removed once that assembly is completed, as issymbolized by the spaced apart spacer shown in phantom. Nevertheless, itis shown as being connected in FIG. 1 to indicate the relation betweenthe seal arrangement elements. Removal of spacer 144 after completion ofassembly does not change the relative positions of those elements.

The materials comprising specific elements are commercially availableand in most respects standard in the sealing industry. In the preferredembodiment, each of the primary rings 36, 64 are carbon graphite ringsand the mating rings 40,60 are silicon carbide or tungsten carbide. Thespring 80 is stainless spring steel and the liner, the gland plate 30,the sleeve 32, the collar 52, the spacer 144 and the various cap and setscrews may all comprise an appropriate steel, such as 316 stainlesssteel.

The O-rings which are exposed to a process fluid, which in most cases isintended to be corrosive or toxic. Thus, the O-rings must comprise amaterial which is relatively impervious or chemically resistant to amajority of corrosive fluids. Accordingly, O-rings 47,56 and 58 comprisea chemically resistant elastomer, such as perfluoroelastomer. Theexpense of this material precludes its extensive use for all of theO-rings throughout the seal arrangement. O-rings 70, 75 and 138 each maycomprise an elastomeric material which is generally used for O-rings,such as a fluorocarbon elastomer, chloroprene, ethylene propylene ornitrile. During normal operation of the seal arrangement, the O-rings70, 75 and 138 are not exposed to the corrosive process fluid, and thusthere is no requirement of a chemically resistant or imperviouselastomeric material for those O-rings.

The assembly of the seal arrangement 10 must proceed in accordance witha predetermined procedure. The preferable construction of the sealarrangement 10 is as a cartridge permitting assembly of a majority ofthe seal off-site from where the seal will be used. Thus, the onlyon-site assembly which would be required in that case would be theinstallation of the seal arrangement cartridge, connecting the glandplate 30 to the housing 12 and adjusting the axial position of thesleeve 32.

Assembly of the cartridge at an off-site manufacturing plant would beginby disposing the disc 84 in one end of the retainer 90 and sliding thedisc toward the retainer central disk portion 96. The O-ring 70 is thenfit within the annular shoulder 84 of primary ring 64 and the primaryring 64 is placed into the retainer 90 with the face opposite the sealface 66 abutting the disc 84. Snap ring 100 is then disposed withingroove 98 to retain the primary ring 64 within the retainer 90.

The next step is sliding the retainer 90 together with the primary ring64, the disc 84 and the O-ring 70 over a sleeve 32 from the end withthinner portion 51 toward the thicker portion 50, until the innerdiameter of the disc 84, the O-ring 70 and the inner diameter of theprimary ring 64 engage the outer diameter of the sleeve thicker portion50.

The springs 80 are then placed in the appropriate bores 94, around theretainer central disc portion 96 from the other end of the retainer 90so that the springs 80 engage the disc 84. Disc 82 is then slid from theother end of the retainer 90 until the disc contacts the spring 80.O-ring 58 is disposed within the outer diameter groove of sleeve 32 andprimary ring 36 is inserted within the opposite end of the retainer 90so that the back face, opposite from sealing face 38 contacts the disc82. Care must be taken in the insertion of primary ring 36 so as toavoid squeezing or catching an inner diameter corner of the ring 36 onthe O-ring 58.

After the back face of the primary ring 36 clears the O-ring 58, theprimary ring 36 and disc 82 compress the springs 80 to some extent. Asecond snap ring 100 is fit within the groove 98 at the opposite endfrom the first snap ring, thus retaining both primary rings 36,64 withinthe retainer 90. The springs 80 will bias the primary rings 36, 64outwardly until the respective shoulders 72,37 engage the snap rings100.

The thicker portion 50 of sleeve 32 is then axially centered within thespace defined by the primary rings 36,64 and a plurality of set screws(not shown) is inserted in equidistantly disposed radial bores (notshown) both in the retainer center disk portion 96 and the sleevethicker portion 50 to connect the retainer 90 to the sleeve 48 and tofix the retainer 90 in the axial and circumferential directions forrotation with the sleeve. The O-ring 56 can be inserted into the innergroove of sleeve 32 at any time when convenient.

The liner assembly 28 together with retaining pin 43, which duringmanufacture has been press fit within the bore 112 of the liner assemblyinner diameter portion 110, is brought up. O-ring 47 is fit withingroove 114 and the mating ring 40 is inserted into the liner assembly sothat the non-sealing faces on the opposite side of mating ring 40 fromthe face 42 engage the liner assembly inner diameter portion 110 and thepin 43 is inserted within the bore 41 of mating ring 40. Care must betaken to ensure that the O-ring 45 does not interfere with the insertionof the mating ring 40.

The next assembly step is fitting O-ring 75 around the outercircumferential groove 77 of mating ring 60, and fitting the mating ring60 within the gland plate 30 so that the outer circumferential surfaceof mating ring 60 engages the surface 132 of the gland plate 30. AnO-ring 138 is disposed in the groove 139 of the gland plate.

The retainer 90 together with all of the appurtenant elements includingprimary rings 36, 64 and sleeve 32 is then positioned within the linerassembly 28 so that the sealing face 42 of the mating ring 40 engagesthe sealing face 38 of primary ring 36. The gland plate 30, togetherwith the mating ring 60 is then slid over the thinner portion 51 ofsleeve 32 until the sealing faces 62 and 66 engage.

The thicker portion 50 of sleeve 32 is then axially centered within thespace defined by the primary rings 36, 64 and a plurality of set screws(now shown) is inserted in equidistantly disposed bores (not shown) bothin the retainer center disc portion 96 and the sleeve thicker portion 50to connect the retainer 90 to the sleeve 32 and to fix the retainer 90in the axial and circumferential directions for rotation with thesleeve. The O-ring 56 can be inserted into the inner groove of sleeve 32at any time when convenient.

A gap should become apparent between the liner assembly outer diameterflange portion 120 and the gland plate 30 which results from the springs80 being in an extended condition, thus biasing the primary rings 36, 64to the limit of the retainer position permitted by snap rings 100. Thegland plate 30 is then positioned relative to the bores of the outerdiameter flange portion 120 to maintain alignment for insertion of thebolts 148 which will connect the assembly to the housing 12. The glandplate 30 is then depressed in the axial direction thus pushing towardseach other the primary rings 36, 64 while compressing the springs 80.Insertion and tightening of bolts 130 connects the liner assembly 28 tothe gland plate 30, and defines the position of the primary rings 36, 64within the two mating seal faces 42,62. However, the sleeve 32 togetherwith the retainer 90, are axially slidable relative to the position ofthe primary rings 36, 64.

Once the bolts 130 are tightened and the gland plate 30 is connected tothe outer diameter flange portion 120 of liner assembly 28, the sealarrangement 10 is ready for installation on to a shaft 16. A set ofspacers 144 is first connected to the outer radial wall of the glandplate at an appropriate radius from the center line by screwing capscrews (not shown) through the radially extending leg of each spacer 144into the bores in the gland plate 30. The collar 52 is then slipped intothe space defined by the other, axially extending leg of each spacer 144and cap screws attach the spacers 144 to the collar 52. The sealarrangement can then be shipped to an installation site.

A repeller pump (not shown) may be considered as an appropriate examplefor installation of the seal arrangement. The motor of such a pump (notshown) which would be connected to the shaft 16 at the right side ofFIG. 1, would first be disconnected. Any material, such as old packing,would be withdrawn from the stuffing box defined by housing 12, and thesurfaces of the shaft, stuffing box and wall 12 would be cleaned ofdebris or corrosion, if necessary. The seal arrangement, as a cartridgewould then be carefully inserted so that the outer diameter wall of theliner assembly inner diameter portion 110 fit within the stuffing boxdefined by the wall of housing 12, while simultaneously the sleeve 32fit over the shaft 16. Care must be taken to ensure that the O-ring 56does not interfere with the slidability of sleeve 32 along the shaft 16.

The seal arrangement cartridge 10 is then slid along the shaft 16 untilthe radial wall 126 of the liner assembly outer diameter flange portion120 engages the radial wall of housing 12 while simultaneouslycompressing O-ring 122 to effect a seal therebetween.

Bolts 148 are then inserted into the appropriate bores through the glandplate 30 and liner assembly outer diameter flange portion 120 andscrewed into the threaded bore 150 in the radial wall of housing 12. Thebolts 148 fix the stationary portions of the seal arrangement cartridge10 relative to the housing 12; while the sleeve assembly 32, togetherwith the retainer 90 and primary rings 36, 64, are free to move axiallyand to rotate with the shaft.

Axial centering of the sleeve assembly 32 is once again performed by thespacers 144 fixing the position of the sleeve assembly 32 and of theretainer 90 which is connected to the sleeve 48. The spacers 144position the bores 142 through which at the appropriate axial positionrelative to the shaft 16 so that a small rotation of the shaft 16disposes the bores 142 of the collar 52 over threaded bores 146 in shaft16. Set screws 140 are then inserted through the bores 142 of collar 52and bores 143 in sleeve thinner portion 150 and screwed into thethreaded bores 146, thus fixing the position of collar 52 and sleeveassembly 32 relative to the shaft 16. Spacers 144 are then removed byunscrewing the cap screws (not shown) so that the shaft is free torotate relative to the housing.

Operation of the seal arrangement 10 requires the user to provide asource of a relatively insert gas, such as nitrogen or one of the noblegases, as a buffer fluid. The gas should be supplied at a pressure whichexceeds the maximum process fluid pressure by at least 10 p.s.i. Thebuffer gas pressure may exceed the maximum process fluid pressure by amuch greater amount, in which case a regulator may be necessary todecrease the pressure to a desirable level. The supply of the buffer gasis continuously injected into the inlet port 134 and the gas then entersthe intermediate chamber 26 through the connecting passage 136.

During shaft rotation, the assembly comprising the retainer 90, theprimary rings 36, 64 and the sleeve 32 rotates with the shaft 16. Theonly point of direct interface between the rotating elements and thestationary elements, fixed relative to the housing 12, is at theinterface between the seal faces 38,42 and 62,66 of each of therespective seals 22,24. That is, while the mating ring seal faces 42,62remain stationary, the primary ring faces 38,66 are rotating relativethereto.

Introduction of a steady stream of a buffer gas into the intermediatechamber 26 at a pressure exceeding both the maximum process fluidpressure within the housing and the pressure in ambient environmentexternal to the housing, usually atmospheric pressure, forces the buffergas into and through the gap formed by the seal faces during shaftrotation. Thus, the only leakage across the seal faces 38,42 of seal 22is the buffer gas leakage from the intermediate chamber 26 into thehousing chamber 18, and across the seal faces 62,66 of seal 24 is fromthe intermediate chamber 26 into the ambient environment, such asatmosphere 20.

Actual contact between the seal faces is to be avoided during therotation of the shaft, but the gap which develops between the seal facesis small enough to maintain only slight leakage of the buffer fluidthrough each of the seals 22,24. The direct interface between the twosets of seal faces maintains the sealing capacity of one seal betweenthe process fluid contained by the housing and the intermediate chamberand the other seal being between the intermediate chamber and theambient environment external to the housing.

In the preferred embodiment, the spiral grooves 44 on the mating ringseal face 42 also pump the buffer gas from the intermediate chamber 26and into the process fluid chamber 18. Ideally, the pumping action ofthe spiral grooves 44 and the buffer gas pressure act in concert tomaintain all leakage across the seal 22 in the desired direction and toinhibit the escape of toxic or corrosive process fluids into theintermediate chamber 26. Moreover, even if some process fluid does leakinto the intermediate chamber by accident, the positive pressure of thebuffer gas in the other direction would tend to inject the process fluidback into the chamber 18.

The configuration of the seal system together with the positive buffergas pressure prevents most leakage of the process fluid to atmosphere. Afailure of one of the seals would not permit process fluid leakage,because continuous monitoring of the gas pressure in the intermediatechamber 26 would signal the need for a system shutdown in the event thatthe pressure dropped below a predetermined level. For example, if one ofthe seals 22, 24 failed, then there would be an immediate pressure dropin the intermediate chamber, which would cause the system to shut downand a cessation of the rotation of the shaft 16. If it was seal 22 whichfailed, system shutdown would not permit escape of the process fluidfrom the intermediate chamber 26 because of the static seal provided bydam 76 of the seal ring face 62. Conversely, if seal 24 failed, thestatic seal provided by dam 46 of seal ring face 42 would preventprocess fluid from entering the intermediate chamber, thus permittingonly buffer gas to escape from the intermediate chamber.

The advantages provided by the use of the inventive seal arrangementinclude the elimination of a "wet" buffer fluid such as oil, which canbecome messy and may contaminate the process fluid. Moreover, oillubricant is expensive.

In contradistinction, the preferred embodiment of the presentapplication is a dry running seal which has a gas as a lubricant. Whenequipped with spiral grooves, the seal faces separate to create a gapbetween the faces and the use of non-contacting type seals results inlonger seal life and reduces heat generation resulting from contactingfriction. A slight but steady stream of the buffer gas through andacross the seal faces acts as a coolant to remove any heat which may begenerated by viscous shear between the seal faces. Thus, it is notnecessary to circulate the buffer fluid around the seal area since nofrictional heat problem arises.

For use with toxic process fluids, use of nitrogen as a buffer gas isapproved by environmental regulations and agencies. Moreover, becauseseal failure will immediately shut down the system, the seal arrangementaccording to the present invention can be used without constantmonitoring of gas effluent for toxic fluid escape.

The inventive seal arrangement is capable of use in a variety of sealingapplications, including most pumps. For example, the seal can be usedwith repeller pumps which evacuate the space in the housing immediatelyaround the seal rings so as to provide at least a partial vacuum.Nitrogen "consumption", i.e. nitrogen injection into the housingchamber, is reduced in a repeller pump because the partial vacuum causedby the repeller permits a lower nitrogen gas buffer pressure. It isnevertheless preferable to maintain a pressure differential between therepeller chamber and the intermediate chamber at about 10 p.s.i.

Whereas a preferred form of the invention has been shown and described,it will be realized that alterations may be made thereto withoutdeparting from the scope of the following claims.

What is claimed is:
 1. A method for sealing against leakage of processfluid under pressure within a housing along a rotatable shaft extendingthrough a wall of the housing, said method comprising the stepsof:utilizing a seal arrangement having:a first rotary mechanical endface seal including a stationary seal ring for sealing connection to thehousing and a rotary seal ring for sealing connection to the shaft, eachsaid ring having radial surfaces, and each said ring including anannular generally radially extending sealing face, being coextensivewith one of said radial surfaces spaced from at least one other of saidradial surfaces thereof, and in relatively rotating, mating sealingrelation with the sealing face of the other of said rings, one of saidseal rings being axially movable relative to the other; a second rotarymechanical end face seal including a stationary seal ring for sealingconnection to the housing and a rotary seal ring for sealing connectionto the shaft, each said ring having an annular generally radiallyextending sealing face in relatively rotating, mating sealing relationwith the face of the other of said rings, one of said seal rings of saidsecond rotary mechanical end face seal being axially movable relative tothe other said seal ring independently of the axial movement of theaxially moveable ring of said first rotary mechanical end face seal;said first and second rotary mechanical end face seals including meansdirectly biasing each of the axially moveable rings toward itsassociated stationary ring to maintain said annular sealing face of saidaxially moveable ring in said relatively rotating sealing relation tosaid annular sealing face of said stationary ring; said first and secondrotary mechanical end face seals being axially spaced apart along theshaft and arranged to define, with said housing, an intermediate chambertherebetween; the relatively rotatable seal rings of said first rotarymechanical end face seal having a first annular circumference of saidsealing faces exposed to the process fluid to be sealed within thehousing, and a second annular circumference of said sealing facesexposed to said intermediate chamber; the relatively rotatable sealrings of said second rotary mechanical end face seal having a firstannular circumference of said sealing faces exposed to said intermediatechamber, and a second annular circumference of said sealing facesexposed to the ambient environment external to said housing; saidintermediate chamber including means for connection to a source ofrelatively inert gas barrier fluid at a gas barrier fluid pressureexceeding the pressure of said process fluid present at said annularseal face first circumference of said first rotary mechanical end faceseal rings; said first rotary mechanical end face seal includinggap-maintaining means to cause said seal to operate, during shaftrotation, as a gas lubricated, non-contacting seal in the presence ofsaid gas barrier fluid at said gas barrier fluid pressure; and saidfirst rotary mechanical end face seal further including means to causesaid seal to operate, during shaft rotation, as a contacting seal in theabsence of said gas barrier fluid pressure; supplying a relatively inertgas barrier fluid to said intermediate chamber at a gas barrier fluidpressure exceeding the pressure of said process fluid present at saidannular seal face first circumference of said first rotary mechanicalend face seal rings; operating said first rotary mechanical end faceseal, during shaft rotation, in the presence of said gas barrier fluidpressure as a gas lubricated, non-contacting seal, and essentiallyeliminating thrust forces acting on said first rotary mechanical endface seal, by providing said first rotary mechanical end face seal witha first secondary sealing means disposed between one of said seal ringsand the housing for providing a sealing connection therebetween and asecond secondary sealing means disposed between the other seal ring andthe shaft for providing a sealing connection therebetween, to define theboundary between said intermediate chamber and said process fluid withinsaid housing, and sizing and disposing said first and second secondarysealing means of said first rotary mechanical end face seal to defineradial walls in said other radial surfaces and thereby presentingessentially an equal area at an approximately identical radius, suchthat the essentially same amount of buffer fluid pressure acts on theradial surfaces of each of said rings of said first rotary mechanicalend face seal but in opposite directions and on the process fluid side,the identical process fluid pressure thereby acting on opposite sides ofa portion of each of said respective rings of said first rotarymechanical end face seal to essentially eliminate thrust forces actingon said first rotary mechanical end face seal.
 2. A method as claimed inclaim 1 wherein said source of relatively inert gas supplies to theintermediate chamber a relatively inert gas which comprises at least onegas taken from the group of nitrogen, carbon dioxide, air or one of thenoble gases.
 3. A method as claimed in claim 1 wherein said first andsecond mechanical end face seals are provided preassembled together as acartridge and are installed as a unit.
 4. A seal arrangement for sealingagainst leakage of process fluid under pressure within a housing processfluid chamber along a rotatable shaft extending through a wall of thehousing, said seal arrangement comprising:a first rotary mechanical endface seal including a stationary seal ring for sealing connection to thehousing and a rotary seal ring for sealing connection to the shaft, eachsaid ring having a radial surface including an annular generallyradially extending sealing face and at least one other radial surface,said sealing face spaced from the other of said radial surfaces thereof,and said sealing face being in relatively rotating, mating sealingrelation with the sealing face of the other of said rings, one of saidrings being axially moveable relative to the other; a second rotarymechanical end face seal including a stationary seal ring for sealingconnection to the housing and a rotary seal ring for sealing connectionto the shaft, each said ring having an annular generally radiallyextending sealing face in relatively rotating, mating sealing relationwith the face of the other of said rings, one of said seal rings beingaxially movable relative to the other said seal ring independently ofthe axially moveable ring of said first rotary mechanical end face seal;said first and second rotary mechanical end face seals including meansdirectly biasing each of the axially moveable rings toward itsassociated stationary ring to maintain said annular sealing face of saidaxially moveable ring in said relatively rotating sealing relation withsaid annular sealing face of said stationary ring; said first and secondrotary mechanical end face seals being axially spaced apart along theshaft and arranged to define, with said housing, an intermediate chambertherebetween; the relatively rotatable seal rings of said first rotarymechanical end face seal having a first annular circumference of saidsealing faces exposed to the process fluid to be sealed within thehousing process fluid chamber, and a second annular circumference ofsaid sealing faces exposed to said intermediate chamber; the relativelyrotatable seal rings Of said second rotary mechanical end face sealhaving a first annular circumference of said sealing faces exposed tosaid intermediate chamber, and a second annular circumference of saidsealing faces exposed to the ambient environment external to saidhousing; said intermediate chamber including means for connection to asource of relatively inert buffer gas at a pressure exceeding thepressure of said process fluid present at said circumference of saidsealing faces exposed to the process fluid; said first rotary mechanicalend face seal including gap maintaining means defined by said relativelyrotating sealing faces to maintain said seal faces at a gap during shaftrotation in the presence of said buffer gas at said pressure exceedingthe pressure of said process fluid present at said circumference of saidsealing faces exposed thereto; said first rotary mechanical end faceseal further including a first secondary sealing means disposed betweenone of said seal rings and the housing for sealing therebetween and asecond secondary sealing means disposed between the other of said sealrings and the shaft for sealing therebetween, said first and secondsecondary sealing means each defining the boundary between saidintermediate chamber and said process fluid chamber, said first andsecond secondary sealing means of said first rotary mechanical end faceseal being sized and disposed to define radial walls in said otherradial surfaces to thereby present essentially an equal area at anapproximately identical radius, such that essentially the same amount ofbuffer fluid pressure acts on said other radial surfaces of each of saidrings of said first rotary mechanical end face seal but in oppositedirections and, on the process fluid side, the identical process fluidpressure acts on opposite sides of a portion of said respective rings ofsaid first rotary mechanical end face seal essentially eliminatingthrust forces acting on said first rotary mechanical end face seal. 5.The seal arrangement as claimed in claim 4 wherein said first and secondsecondary sealing means include an O-ring disposed in sealing relationbetween said stationary seal ring and one of said housing and shaft andan O-ring disposed in sealing relation between said rotary seal ring andthe other of said housing and shaft.
 6. The seal arrangement as claimedin claim 5 wherein said gap maintaining means comprises a plurality ofgrooves formed on one of said relatively rotating sealing facesextending from said circumference exposed to said intermediate chambertoward said other circumference, said one of said relatively rotatingsealing faces further defining a sealing dam between said grooves andsaid other circumference.
 7. The seal arrangement as claimed in claim 6wherein said grooves are spiral grooves.
 8. The seal arrangement asclaimed in claim 5 wherein said secondary sealing means associated withsaid axially moveable seal ring includes a radial wall associated withsaid one of said shaft and housing, said radial wall being in fixedaxial position and disposed adjacent said O-ring in sealing relationbetween said axially moveable ring and said one of said shaft andhousing.
 9. The seal arrangement as claimed in claim 6 wherein saidsecondary sealing means associated with said axially moveable seal ringincludes a radial wall associated with said one of said shaft andhousing, said radial wall being in fixed axial position and disposedadjacent said O-ring in sealing relation between said axially moveablering and said one of said shaft and housing.
 10. The seal arrangement asclaimed in claim 7 wherein said secondary sealing means associated withsaid axially moveable seal ring includes a radial wall associated withsaid one of said shaft and housing, said radial wall being in fixedaxial position and disposed adjacent said O-ring in sealing relationbetween said axially moveable ring and said one of said shaft andhousing.
 11. The seal arrangement of claim 4 said axially moveable ringof said first rotary mechanical end face seal further includes aradially extending surface spaced from said radial sealing face, saidsurface being exposed to the pressure of the process fluid in saidprocess fluid chamber.
 12. The seal arrangement of claim 5 said axiallymoveable ring of said first rotary mechanical end face seal furtherincludes a radially extending surface spaced from said radial sealingface, said surface being exposed to the pressure of the process fluid insaid process fluid chamber.
 13. The seal arrangement of claim 6 saidaxially moveable ring of said first rotary mechanical end face sealfurther includes a radially extending surface spaced from said radialsealing face, said surface being exposed to the pressure of the processfluid in said process fluid chamber.
 14. The seal arrangement of claim 7said axially moveable ring of said first rotary mechanical end face sealfurther includes a radially extending surface spaced from said radialsealing face, said surface being exposed to the pressure of the processfluid in said process fluid chamber.
 15. The seal arrangement of claim 8said axially moveable ring of said first rotary mechanical end face sealfurther includes a radially extending surface spaced from said radialsealing face, said surface being exposed to the pressure of the processfluid in said process fluid chamber.
 16. The seal arrangement of claim 8said axially moveable ring of said first rotary mechanical end face sealfurther includes a radially extending surface spaced from said radialsealing face, said surface being exposed to the pressure of the processfluid in said process fluid chamber.
 17. The seal arrangement of claim10 said axially moveable ring of said first rotary mechanical end faceseal further includes a radially extending surface spaced from saidradial sealing face, said surface being exposed to the pressure of theprocess fluid in said process fluid chamber.
 18. A seal arrangement asclaimed in claim 4 wherein said relatively inert gas is taken from thegroup consisting of nitrogen, carbon dioxide, air and a noble gas.
 19. Aseal arrangement as claimed in claim 4 wherein said gap maintainingmeans on the seal face of one of said rings of said first rotarymechanical end face seal are formed on said stationary seal ring.
 20. Aseal arrangement as claimed in claim 19 wherein said stationary sealring sealed against the housing of said first rotary mechanical end faceseal is a mating ring and said rotary seal ring sealed against saidshaft is an axially moveable primary ring which is biased by saidbiasing means.
 21. A seal arrangement as claimed in claim 6 wherein saidgrooves on the seal face of one of said rings of said first rotarymechanical end face seal extend from the outer diameter toward the innerdiameter of said seal ring face and the dam is adjacent the innerdiameter of said seal ring face.
 22. The seal arrangement of claim 4further comprising a sleeve sealingly connected to said shaft, saidsleeve being disposed between said shaft and said axially moveable ringof said first rotary mechanical end face seal, said axially moveablering being disposed around said sleeve, said axially moveable ringrotating with said shaft and said sleeve, one of said second secondarysealing means providing a seal between a cylindrical surface of saidaxially moveable ring and said sleeve while permitting axial movement ofsaid axially moveable ring relative to said sleeve, and said sealarrangement including at least one radially extending secondary sealwall retained in fixed axial position relative to said sleeve.
 23. Aseal arrangement as claimed in claim 22 wherein said first and secondseals are preassembled as a cartridge for installation.
 24. A sealarrangement as claimed in claim 23 wherein said means biasing each ofthe axially moveable rings toward the other for each of said first andsecond rotary mechanical end face seals comprises a common spring whichbiases each of the axially moveable rings outwardly from a locationcentral to both of said axially moveable rings.
 25. A seal arrangementas claimed in claim 21, wherein the radial face of one of said rings ofsaid second rotary mechanical end face seal includes a plurality ofgrooves extending from said circumference exposed to said intermediatechamber partially toward said circumference exposed to the ambientenvironment external to said housing and defining an annular damadjacent said circumference exposed to the ambient environment externalto said housing.
 26. A seal arrangement as claimed in claim 25 whereinsaid grooves on the seal face of one of said rings of said second rotarymechanical end face seal extend from the outer diameter toward the innerdiameter of said seal ring face and the dam is adjacent the innerdiameter of said seal ring face.